Fig. 2.

Similar facilitatory effects of 5-HT on commissural interneurons activated from RF and by group II afferents. (A and C) Top pair of records are single sweep records from an interneuron monosynaptically activated by RF fibres and from the cord dorsum. The traces below are peri-stimulus time histograms (PSTH) of responses to 20 stimuli. They were complied from stimuli delivered before (control), during (15s, 1 and 2min) and after ionophoresis of 5-HT (Rec., 5 min after withdrawal of the ionophoretic pipette). (B and D) The same format as in A and C but for an interneuron activated by stimulation of group II afferents in the Q nerve. Dotted vertical lines in C and D indicate the minimal latency in the control records. The dotted horizontal lines in A and B indicate the discrimination levels; only spikes crossing these lines were used for construction of PSTHs. (E and F) Collision tests for the neurons in A and B, respectively. The records show that antidromic spikes from the contralateral GS motor nucleus collided with synaptically evoked responses at intervals shorter than twice the conduction time from this nucleus. Shock artefacts truncated. Time calibrations as indicated.